Three-dimensional electron spin resonance imaging of endogenous nitric oxide radicals generated in living plants

Abstract

Electron spin resonance imaging (ESRI) has been developed to detect the spatial contribution of free radicals in recent years, but all of these studies are used in animal systems and almost of them using exogenous spin probes and only a few to study the endogenous free radicals in vivo. However, there is no report about the endogenous free radical three-dimensional (3D) EPRI in plant because of low concentration of endogenous free radicals and low resolution of the L-band ESRI. Recently, we have developed the imaging resolution better than 200 μm which is higher 10 times than L-band (about 1–3 mm) and the sensitivity is higher about 1000 times than that of L-band ESRI. Using this system and spin trapping technique, we studied spatial contribution of the endogenous nitric oxide (NO) radical generation in wheat leaves and got a clear 3D ESRI picture and CT (computed tomography) of NO of a wheat leaf. This imaging picture shows a clear spatial distribution of NO free radicals in the leaf. This is the first 3D ESRI of endogenous NO free radical generated in plant in the world. We have also studied the distributions of NO generation in different plants from different species with different shapes and it is shown that this is a convenient method to study the endogenous free radicals in plants.